One of the main responsibilities of an anesthesiologist or nurse anesthetist during a surgical procedure is the management of a patient's nociception level (i.e. pain) via the administration of analgesia (typically fast acting opioid analgesics, e.g., Remifentanil, Sufentanil, Fentanyl). Pain management is important for humanitarian reasons, to help in improving the efficacy of many general anesthetics and because of significant physiological benefits (cf. Stomberg M W, et al. Assessing pain response during general anesthesia, AANA Journal 2001, 69(3):218-222). This latter point is important, since although the patient is unconscious during the surgical procedure, they still experience a physiological ‘stress’ response to the nociceptive stimuli (e.g. surgical incision, intubation) which involves activation of the body's vasomotor Sympathetic Nervous System (SNS) and inhibition of the cardiac Parasympathetic Nervous System (PNS).
In addition, pain management is also important in the post-operative period since it has implications for patient recovery and discharge from hospital (Pyati S, Gan T J., Perioperative pain management, CNS Drugs. 2007, 21(3):185-211). Pain management is required since during surgery patients must not be in pain but over-dosing of analgesic agents must be avoided. In the post-operative period administration of too much pain drugs or too little has important implications for patient recovery and discharge from hospital. Despite the recognition of the importance of effective pain control, up to 70% of patients still complain of moderate to severe pain postoperatively. Pain management has also become increasingly important since pain level is a key indicator used to assess the quality of care delivered by a hospital. Despite the importance of pain management during the perioperative period, there are very few products that offer an objective method for the assessment of the pain (i.e. nociception) level and, by extension, depth of analgesia level of a patient, especially intra- and post-operatively. These products mainly focus on how vital signs react to nociceptive stimuli. Pain management is also of great importance to intensive care units (ICU), neonatal intensive care units and patients in the general ward and at home who could experience periods of pain.
One approach to the monitoring of sedated patients includes the anesthesiologist manually adjusting the analgesia depth (i.e. the drug administration) based on an observation of patient movement and changes in three key parameters in response to nociceptive stimuli: heart rate (HR), non-invasive systolic blood pressure (NISBP) and bispectral index (BIS), which is an indicator of the sedation or hypnosis level as illustrated in FIG. 3. The anesthesiologist also observes patient reactions, like sweating, eye twitching and slight movements. Any of these could indicate inadequate analgesia.
Presently, in the operating room (OR), an anesthesiologist usually observes patient movement and changes in parameters like the heart rate, the blood pressure etc. for monitoring the pain level of a patient and for adjusting the analgesia depth. Also the blood Pressure, pulse Rate, Sweating, Tears (PSRT) algorithm as illustrated in FIG. 4 is widely used to monitor the pain level and depth of analgesia. The drawbacks of both of these approaches are that they are highly subjective, rely heavily on the experience of the clinician and are reactive to changes in patient condition, rather than being pre-emptive or predictive.
The drawbacks of both of these approaches are that they are highly subjective, rely heavily on the experience of the clinician and are reactive to changes in patient condition, rather than being pre-emptive or predictive.
An approach for providing an objective measurement is pupillometry. Traditionally, the healthcare professional observes the pupil size with the naked eye. Alternatively, automated video-pupillometry involves camera observation of the eye and automatic image analysis to segment out the iris, followed by determination of pupil diameter and, if needed, the quantification of the effect of a stimulus in percent. Video-pupillometry is the preferred method for scientific research and analysis of drowsiness. This, however, requires direct video access. Therefore, it cannot be performed continuously (i.e., it provides only a point measurement) and is unsuitable for use during surgery (eyes of the patient are taped shut to prevent drying out and corneal abrasion); sleep (closed eyes and movement) and use during the day (movement).
Although pupillometry is an established diagnostic approach to assess pain and brain function, a use in the OR during general anesthesia of a patient has so far been limited. One reason for this is that current pupillometry devices do not allow performing pupillometry if the eyes of the patient are closed. During prolonged general anesthesia this is, however, usually the case. For instance, visual access to the eye is not available during an operation generally since the eyes are taped shut and/or cream is applied to prevent dehydration of the eyes. Also, pupillometry is usually a hands-on activity (which would require an additional person in the OR) to hold the device and open up the eyes. Therefore, pupillometry is mostly used in the form of a spot-check measurement to determine a current state of the patient. Furthermore, excessive use of wires and devices touching the patient may decrease freedom of action for the surgery team. Current devices are often cumbersome and bulky and not very practical for an OR environment. Further, often additional components for preventing dehydration of the eye are required.
Another monitoring approach is based on pupillometry, which involves the measurement of pupil dilation, oscillations in pupil size, and pupillary light reflex amplitude (i.e. the difference between pupil dilation before and after light stimulation). A drawback of this method is that it cannot be performed continuously (i.e. it provides only a point measurement) and therefore is unsuitable for use during surgery. Another drawback of the use of pupillometry is that the eyes of a patient are typically taped shut during surgery to prevent them from drying out and avoid corneal abrasion.
In US 2014/0185010 A1 a method of monitoring the pupil of a subject is disclosed. A sensor for observing the pupil is arranged between the cornea and the eyelid covering the cornea, the sensor is powered through the eyelid, and the pupil-observation signals delivered by the sensor are collected through the eyelid.
There is, however, still a need for improving anesthesia and pain monitoring solutions for being applied during anesthesia, in particular with respect to accuracy and reliability.